The present invention relates generally to lofty nonwoven fiber webs. The present invention relates specifically to lofty nonwoven fiber webs of homofilament crimped fibers and means for utilizing the web in its lofty and uncompressed state to retain the advantages of web structure.
Webs of homofilament crimped thermoplastic fibers are useful for various fluid handling or retaining materials and the like because of their open structure, resiliency, and economy of manufacture. Particularly, the use of a single thermoplastic polymer in the making of the crimped fibers is good for economical and consistent manufacture. However, one may lose the benefit of the lofty crimped fiber web structure if the homofilament crimped web is processed by known means. Because a homofilament crimped web is usually loosely bonded, such means will include compaction of the web or exposure to high heat, in order to increase the integrity of the web for later processing. Compaction, as in Jacobs et al., U.S. Pat. No. 5,810,954, will decrease bulk or loft of the web through mechanical action as the web is drawn between compaction rollers. Also, this type of processing may result in mechanical failure of the rollers as the filaments become entangled in the mechanical works of the rollers.
In another known means of increasing web integrity, exposure to high heat in an effort to provide thermal bonding between filaments of the web, as in the hot air knife (HAK) teaching of U.S. Pat. No. 5,707,468 to Arnold et al., will result in relaxation of the fiber crimp with resultant loss of bulk for the web.
Conversely, it has been found that the crimps of a homofilament crimped thermoplastic fiber web may be crystallized, or set, to retain their loft through low applications of heat as in U.S. Pat. No. 6,123,886 to Slack. However this treatment does little to increase the integrity of the web for modem, high-speed, line-transfer manufacturing, and as taught in Slack, is a slow, off-line process unsuitable for economical manufacture rates.
Therefore, there is a need in the art for methods and materials utilizing the lofty crimped homofilament nonwoven web with high loft intact and with sufficient integrity to the lofty crimped web to enable high speed manufacturing processes to achieve economy.
Within the context of this specification, each term or phrase below will include the following meaning or meanings.
xe2x80x9cArticlexe2x80x9d refers to a garment or other end-use article of manufacture, including but not limited to, diapers, training pants, swim wear, catamenial products, medical garments or wraps, and the like.
xe2x80x9cBondedxe2x80x9d or xe2x80x9cbondingxe2x80x9d refers to the joining, adhering, connecting, attaching, or the like, of two elements. Two elements will be considered to be bonded together when they are bonded directly to one another or indirectly to one another, such as when each is directly bonded to intermediate elements.
xe2x80x9cConnectedxe2x80x9d refers to the joining, adhering, bonding, attaching, or the like, of two elements. Two elements will be considered to be connected together when they are connected directly to one another or indirectly to one another, such as when each is directly connected to intermediate elements.
xe2x80x9cCross direction assemblyxe2x80x9d refers to a process in which disposable absorbent products are manufactured in an orientation in which the products are connected side-to-side, in the transverse direction shown by arrow 49 in FIG. 3, a process utilizing a cross direction assembly entails products traveling through a converting machine parallel to the direction of arrow 49, as opposed to xe2x80x9cmachine direction assemblyxe2x80x9d in which the products are connected end-to-end or waist-to-waist.
xe2x80x9cDisposablexe2x80x9d refers to articles which are designed to be discarded after a limited use rather than being laundered or otherwise restored for reuse.
xe2x80x9cDisposed,xe2x80x9d xe2x80x9cdisposed on,xe2x80x9d and variations thereof are intended to mean that one element can be integral with another element, or that one element can be a separate structure bonded to or placed with or placed near another element.
xe2x80x9cFabricsxe2x80x9d is used to refer to all of the woven, knitted and nonwoven fibrous webs.
xe2x80x9cFilmxe2x80x9d refers to a thermoplastic film made using a film extrusion and/or foaming process, such as a cast film or blown film extrusion process. The term includes apertured films, slit films, and other porous films which constitute liquid transfer films, as well as films which do not transfer liquid.
xe2x80x9cFlexiblexe2x80x9d refers to materials which are compliant and which will readily conform to the general shape and contours of the wearer""s body.
xe2x80x9cHomofilamentxe2x80x9d refers to a fiber formed from only one predominate polymer and made from a single stream of that polymer. This is not meant to exclude fibers formed from one polymer to which small amounts of additives have been added for coloration, anti-static properties, lubrication, hydrophilicity, etc.
xe2x80x9cIntegralxe2x80x9d or xe2x80x9cintegrallyxe2x80x9d is used to refer to various portions of a single unitary element rather than separate structures bonded to or placed with or placed near one another.
xe2x80x9cLayerxe2x80x9d when used in the singular can have the dual meaning of a single element or a plurality of elements.
xe2x80x9cLiquid impermeable,xe2x80x9d when used in describing a layer or multi-layer laminate, means that a liquid, such as urine, will not pass through the layer or laminate, under ordinary use conditions, in a direction generally perpendicular to the plane of the layer or laminate at the point of liquid contact. Liquid, or urine, may spread or be transported parallel to the plane of the liquid impermeable layer or laminate, but this is not considered to be within the meaning of xe2x80x9cliquid impermeablexe2x80x9d when used herein.
xe2x80x9cLiquid permeable materialxe2x80x9d or xe2x80x9cliquid water-permeable materialxe2x80x9d refers to a material present in one or more layers, such as a film, nonwoven fabric, or open-celled foam, which is porous, and which is water permeable due to the flow of water and other aqueous liquids through the pores. The pores in the film or foam, or spaces between fibers or filaments in a nonwoven web, are large enough and frequent enough to permit leakage and flow of liquid water through the material.
xe2x80x9cLongitudinalxe2x80x9d and xe2x80x9ctransversexe2x80x9d have their customary meaning, as indicated by the longitudinal and transverse axes depicted in FIG. 3. The longitudinal, or long, axis lies in the plane of the article and is generally parallel to a vertical plane that bisects a standing wearer into left and right body halves, when the article is worn. The transverse axis lies in the plane of the article generally perpendicular to the longitudinal axis. The article, although illustrated as longer in the longitudinal direction than in the transverse direction, need not be so.
xe2x80x9cMachine directionxe2x80x9d refers to the length of a fabric in the direction in which it is produced, as opposed to xe2x80x9ccross directionxe2x80x9d which refers to the width of a fabric in a direction generally perpendicular to the machine direction.
xe2x80x9cMachine direction assemblyxe2x80x9d refers to a process in which disposable absorbent products are manufactured in an orientation in which the products are connected end-to-end or waist-to-waist, in the longitudinal direction shown by arrow 48 in FIG. 3, a process utilizing a machine direction assembly entails products traveling through a converting machine parallel to the direction of arrow 48, as opposed to xe2x80x9ccross direction assemblyxe2x80x9d in which the products are connected side-to-side.
xe2x80x9cMeltblown fiberxe2x80x9d means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity heated gas (e.g., air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than about 0.6 denier, and are generally self bonding when deposited onto a collecting surface. Meltblown fibers used in the present invention are preferably substantially continuous in length.
xe2x80x9cMeltspunxe2x80x9d refers generically to a fiber which is formed from a molten polymer by a fiber-forming extrusion process, for example, such as are made by the meltblown and spunbond processes.
xe2x80x9cMemberxe2x80x9d when used in the singular can have the dual meaning of a single element or a plurality of elements.
xe2x80x9cNonwovenxe2x80x9d and xe2x80x9cnonwoven webxe2x80x9d refer to materials and webs of material which are formed without the aid of a textile weaving or knitting process.
xe2x80x9cPermanently bondedxe2x80x9d refers to the joining, adhering, connecting, attaching, or the like, of two elements of an absorbent garment such that the elements tend to be and remain bonded during normal use conditions of the absorbent garment.
xe2x80x9cPolymersxe2x80x9d include, but are not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term xe2x80x9cpolymerxe2x80x9d shall include all possible geometrical configurations of the material. These configurations include, but are not limited to isotactic, syndiotactic and atactic symmetries.
Words of degree, such as xe2x80x9cAboutxe2x80x9d, xe2x80x9cSubstantiallyxe2x80x9d, and the like are used herein in the sense of xe2x80x9cat, or nearly at, when given the manufacturing and material tolerances inherent in the stated circumstancesxe2x80x9d and are used to prevent the unscrupulous infringer from unfairly taking advantage of the invention disclosure where exact or absolute figures are stated as an aid to understanding the invention.
xe2x80x9cSpunbond fiberxe2x80x9d refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine capillaries of a spinnerette having a circular or other configuration, with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartmann, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No. 3,542,615 to Dobo et al., each of which is incorporated herein in its entirety by reference. Spunbond fibers are quenched and generally not tacky when they are deposited onto a collecting surface. Spunbond fibers are generally continuous and often have average deniers larger than about 0.3, more particularly, between about 0.6 and 10.
xe2x80x9cStretchablexe2x80x9d means that a material can be stretched, without breaking, to at least 150% of its initial (unstretched) length in at least one direction, suitably to at least 200% of its initial length, desirably to at least 250% of its initial length.
xe2x80x9cSurfacexe2x80x9d includes any layer, film, woven, nonwoven, laminate, composite, or the like, whether pervious or impervious to air, gas, and/or liquids.
xe2x80x9cThermoplasticxe2x80x9d describes a material that softens when exposed to heat and which substantially returns to a nonsoftened condition when cooled to room temperature.
As used herein the term xe2x80x9ccompaction rollxe2x80x9d means a set of rollers above and below the web to compact the web as a way of treating a just produced spunbond web in order to give it sufficient integrity for further processing, but not the relatively strong bonding of secondary bonding processes like through-air bonding, thermal point bonding and ultrasonic bonding. Compaction rolls slightly squeeze the web in order to increase its self-adherence and thereby its integrity. Compaction rolls may be operated at heated, chilled, or ambient temperatures.
As used herein the term xe2x80x9chot air knifexe2x80x9d or xe2x80x9cHAKxe2x80x9d means a process of pre- or primarily bonding a just produced spunbond web in order to give it sufficient integrity for further processing similar to the function served by compaction rolls, but does not mean the relatively strong bonding of secondary bonding processes like through air bonding, thermal bonding and ultrasonic bonding. A hot air knife is a device which focuses a stream of heated air at a very high flow rate, generally about 1,000 to about 10,000 feet per minute (fpm) (305 to 3050 meters per minute), or more particularly, from about 3,000 to 5,000 feet per minute (915 to 1525 meters per minute) directed at the nonwoven web immediately after its formation. The air temperature is usually in the range of the melting point of at least one of the polymers used in the web, generally between about 200xc2x0 and 550xc2x0 F. (93xc2x0 and 290xc2x0 C.) for the thermoplastic polymers commonly used in spunbonding. The control of air temperature, velocity, pressure, volume and other factors helps avoid damage to the web while increasing its integrity. The HAK""s focused stream of air is arranged and directed by at least one slot of about xe2x85x9 to 1 inches (3 to 25 mm) in width, particularly about xe2x85x9c inch (9.4 mm), serving as the exit for the heated air towards the web, with the slot running in a substantially cross-machine direction over substantially the entire width of the web. In other embodiments, there may be a plurality of slots arranged next to each or separated by a slight gap. The at least one slot is usually, though not essentially, continuous, and may be comprised of, for example, closely spaced holes. The HAK has a plenum to distribute and contain the heated air prior to its exiting the slot. The plenum pressure of the HAK is usually between about 1.0 and 12.0 inches of water (2 to 22 mmHg), and the HAK is positioned between about 0.25 and 10 inches and more preferably 0.75 to 3.0 inches (19 to 76 mm) above the forming wire. In a particular embodiment the HAK plenum""s cross sectional area for cross-directional flow (i.e., the plenum cross sectional area in the machine direction) is at least twice the total slot exit area. Since the foraminous wire onto which spunbond polymer is formed generally moves at a high rate of speed, the time of exposure of any particular part of the web to the air discharged from the hot air knife is less than a tenth of a second and generally about a hundredth of a second in contrast with the through air bonding process which has a much larger dwell time. The HAK process has a great range of variability and controllability of many factors such as air temperature, velocity, pressure, volume, slot or hole arrangement and size, and the distance from the HAK plenum to the web. More detailed information on the hot air knife process may be found in U.S. Pat. No. 5,707,468 issued Jan. 13, 1998, to Arnold et al.
These terms may be defined with additional language in the remaining portions of the specification.
Homofilament crimped fibers will naturally continue crimping until stasis, or equilibrium, is reached in the intrafilament tensions produced during spinning to induce the fiber crimp. A moving, or in-process, web of homofilament crimped fibers is subjected to a flow of diffused hot air processing which will accelerate setting the crimps in the filaments without excessive interfiber bonding, crushing, or relaxing of the crimp. Thus a crimped nonwoven layer may be economically produced which retains its essential characteristics of the lofty structure. The set-crimp web can further be attached or laminated to other material layers for providing various esthetics and functionalities, such as the web integrity necessary for high speed web transfer technology. The crimp setting is desirably produced in an inline process which enables economies of manufacture.
A layer of lofty nonwoven filaments such as e.g., helically crimped homofilaments, is deposited onto a forming belt and treated with sufficient hot air flow to accelerate the fibers"" natural tendency to crimp and to set the crimps without substantial melt bonding or crimp relaxation of the crimped fibers in order to retain the lofty structure of this layer of the laminate. Various web layers, such as a fused spunbond layer for mechanical integrity may then be bonded, such as by thermal point bonding, to create a laminate which retains the essential characteristics of each layer. For example the layers may desirably be bonded together with sufficient integrity to create a laminate that will withstand high speed web transfer processing without harm to the processing equipment or the material.
The crimped fiber material made according to the present invention can be useful for high loft and high bulk applications such as the loop portions of hook and loop fasteners when designed for engageability with the hook portions, or if a natural fabric cloth-like feel is desired, the fibers may be designed to produce fabric of good softness and drape while keeping sufficient bulk and loft to aid in the cloth like feel. The crimped fiber material of the present invention may further be useful for making fabrics which are extensible largely in the cross direction of the resultant nonwovenweb.